The present invention relates to a fuel injection system for direct injection of fuel into the combustion chamber (or chambers) of an internal combustion engine.
It is described in Japanese Patent Application No. 08-312503 that for each combustion chamber of an internal combustion engine, receptacle bore holes for a fuel injection valve can be provided on the cylinder head of the internal combustion engine, so that a spray section of the respective fuel injection valve can be inserted into these bore holes for direct injection of fuel into the respective combustion chamber. The fuel injection valve inserted into the receptacle bore hole in the cylinder head is held down against the relatively high combustion pressure prevailing in the combustion chamber by a hold-down device designed as a clamping claw. To reliably secure the fuel injection valves in the receptacle bore holes, relatively high hold-down forces must be exerted by the clamping claws on the fuel injection valves so that the fuel injection valves will sit relatively securely and immovably in the receptacle bore holes. For the supply of fuel to an inlet section provided on each fuel injection valve with a fuel inlet opening, Japanese Patent Application No. 08-312503 provides for the use of a fuel distributor line connecting the fuel injection valves to a fuel pump. For each fuel injection valve, the fuel distributor line has a receptacle element into which the inlet section of the fuel injection valve can be inserted, so the receptacle element surrounds the inlet section like a cup. To achieve the required seal, the inlet section of each fuel injection valve has a sealing element in the form of an O ring which is in sealing contact with the inside wall of the receptacle element.
Because of the relatively high combustion pressure in each combustion chamber of the internal combustion engine, the hold-down device must exert a relatively high hold-down force to securely lock the fuel injection valves in their respective receptacle bore holes on the cylinder head. However, the resulting rigid attachment of the fuel injection valves on the cylinder head makes it difficult to assemble the fuel distributor line, because there are deviations in position and angle between the inlet sections of the fuel injection valves and the receptacle elements of the fuel distributor line due to the manufacturing tolerances of the receptacle bore holes for the fuel injection valves on the cylinder head, as well as the receptacle elements for the fuel injection valves on the fuel distributor line. This problem is aggravated by the fact that the hold-down force exerted by the clamping claws does not act uniformly over the periphery of the fuel injection valves installed in the receptacle bore holes on the cylinder head, but instead it acts only at points, which results in a slight tilting of the fuel injection valves in the receptacle bore holes. The resulting additional deviations in position and angle on the inlet sections of the fuel injection valves make the assembly of the fuel distributor line even more difficult. The O ring arranged between the inlet section of the fuel injection valve and the receptacle element of the fuel distributor line compensates for the deviations in position and angle only to a very slight and inadequate extent. The deviations in position and angle that occur in practice with the fuel injection system described in Japanese Patent Application No. 08-312503, also result in a risk of fuel leaking from the seal, which does not compensate for the deviations in position and angle, in addition to the disadvantage of difficult assembly.
German Patent Application No. 29 08 095 describes that a fuel injection valve which is not provided for direct injection of fuel can be secured on a fuel distributor line by a retaining strap, and the inlet section of the fuel injection valve can be inserted into the fuel distributor line by a plug-in nipple. This assembly arrangement does not provide for compensation of deviations in position and angle at the connection of the fuel injection valve with the fuel distributor line, nor is it necessary, because the fuel injection valve is not secured rigidly in the receptacle bore hole of the intake pipe in contrast with the assembly of a directly injecting fuel injection valve on the cylinder head, but instead it is freely movable on a sealing element provided in the receptacle bore hole of the intake pipe.
European Patent Application No. 0 491 582 describes that the fuel injection valves on the fuel distributor line can be preassembled on the fuel distributor line before being inserted into the receptacle orifices. However, this conventional fuel injection system is also unsuitable for direct injection of fuel into the combustion chamber of the internal combustion engine, but it is instead intended for indirect injection of fuel into the intake pipe of the internal combustion engine, so that no special requirements have to be set for the position and angle tolerances of the preassembled fuel injection valves.
A fuel injection system according to the present invention has the advantage that deviations in position and angle which occur due to manufacturing tolerances and assembly-related tolerances are reliably compensated. Therefore, the assembly of the fuel injection system, in particular the fuel distributor line, is greatly facilitated. This prevents warping of the fuel injection valves or the fuel distributor line as can occur with a connection that does not compensate for deviations in position and angle. Furthermore, there are no sealing problems between the fuel distributor line and the inlet sections of the fuel injector valves, because the sealing elements are not deformed unilaterally due to uncompensated deviations in position and angle. Conversely, the fuel injection system refined according to the present invention permits greater tolerances in the manufacture of the cylinder head and the fuel distributor line, thereby reducing the manufacturing complexity of these parts and thus reducing manufacturing costs accordingly. The fuel distributor line can be installed relatively close to the cylinder head, so only a small space is needed.
The connecting area between the fuel distributor line and the inlet section of the fuel injection valves may be designed with a relatively large cross section, so there is no drop in pressure when the fuel injection valves are opened.
When using sleeve-shaped securing elements which can be connected to the fuel distributor line and the transition pieces, preferably by a snap catch connection, there is the possibility of preassembly of the transition pieces on the fuel distributor line for a fuel injection system according to one embodiment of the present invention. The fuel distributor line can be removed from the fuel injection valves for maintenance purposes in dismantling together with the transition pieces which are secured on the fuel distributor line by the securing elements. Furthermore, it is advantageous if the transition piece is designed with such a large diameter that a fuel reservoir which compensates for pressure fluctuations is formed upstream from the fuel inlet opening of the respective fuel injection valve. This prevents a pressure drop when opening the fuel injection valve, because the fuel reservoir in the transition piece acts as a buffer storage and also permits unthrottled inflow of fuel from the fuel distributor line to the fuel inlet opening of the respective fuel injection valve.
With a fuel injection system according to another embodiment of the present invention, it is advantageous if the midpoint in the curvature of the cup-shaped supporting face is in the area of a sealing element on which the spray section of the fuel injection valve inserted into the receptacle bore hole is pivotably mounted. This guarantees that the supporting section provided on the fuel injection valve is in complete contact with the cup-shaped supporting face in each swivel position of the fuel injection valve. The cup-shaped supporting face can be advantageously formed on a supporting body which can be inserted into the receptacle bore hole of the cylinder head. This makes it possible to simplify manufacture by designing the supporting body as a separate part, in particular as a separately manufactured turned part, and is manufactured independently of the cylinder head.